Mechanical and chemical-mechanical planarization processes (collectively “CMP”) are used in the manufacturing of electronic devices for forming a flat surface on semiconductor wafers, field emission displays and many other microelectronic device substrate assemblies. CMP processes generally remove material from a substrate assembly to create a highly planar surface at a precise elevation in the layers of material on the substrate assembly. FIG. 1 schematically illustrates an existing web-format-planarizing machine 10 for planarizing a substrate 12. The planarizing machine 10 has a support table 14 with a top-panel 16 at a workstation where an operative portion (A) of a planarizing pad 40 is positioned. The top-panel 16 is generally a rigid plate to provide a flat, solid surface to which a particular section of the planarizing pad 40 may be secured during planarization.
The planarizing machine 10 also has a plurality of rollers to guide, position and hold the planarizing pad 40 over the top-panel 16. The rollers include a supply roller 20, idler rollers 21, guide rollers 22, and a take-up roller 23. The supply roller 20 carries an unused or pre-operative portion of the planarizing pad 40, and the take-up roller 23 carries a used or post-operative portion of the planarizing pad 40. Additionally, the left idler roller 21 and the upper guide roller 22 stretch the planarizing pad 40 over the top-panel 16 to hold the planarizing pad 40 stationary during operation. A motor (not shown) generally drives the take-up roller 23 to sequentially advance the planarizing pad 40 across the top-panel 16, and the motor can also drive the supply roller 20. Accordingly, clean pre-operative sections of the planarizing pad 40 may be quickly substituted for used sections to provide a consistent surface for planarizing and/or cleaning the substrate 12.
The web-format-planarizing machine 10 also has a carrier assembly 30 that controls and protects the substrate 12 during planarization. The carrier assembly 30 generally has a substrate holder 32 to pick up, hold and release the substrate 12 at appropriate stages of the planarizing process. Several nozzles 33 attached to the substrate holder 32 dispense a planarizing solution 44 onto a planarizing surface 42 of the planarizing pad 40. The carrier assembly 30 also generally has a support gantry 34 carrying a drive assembly 35 that can translate along the gantry 34. The drive assembly 35 generally has an actuator 36, a drive shaft 37 coupled to the actuator 36, and an arm 38 projecting from the drive shaft 37. The arm 38 carries the substrate holder 32 via a terminal shaft 39 such that the drive assembly 35 orbits the substrate holder 32 about an axis B—B (as indicated by arrow R1). The terminal shaft 39 may also rotate the substrate holder 32 about its central axis C—C (as indicated by arrow R2).
The planarizing pad 40 and the planarizing solution 44 define a planarizing medium that mechanically and/or chemically-mechanically removes material from the surface of the substrate 12. The planarizing pad 40 used in the web-format planarizing machine 10 is typically a fixed-abrasive planarizing pad in which abrasive particles are fixedly bonded to a suspension material. In fixed-abrasive applications, the planarizing solution is a “clean solution” without abrasive particles because the abrasive particles are fixedly distributed across the planarizing surface 42 of the planarizing pad 40. In other applications, the planarizing pad 40 may be a non-abrasive pad without abrasive particles that is composed of a polymeric material (e.g., polyurethane) or other suitable materials. The planarizing solutions 44 used with the non-abrasive planarizing pads are typically CMP slurries with abrasive particles and chemicals to remove material from a substrate.
To planarize the substrate 12 with the planarizing machine 10, the carrier assembly 30 presses the substrate 12 against the planarizing surface 42 of the planarizing pad 40 in the presence of the planarizing solution 44. The drive assembly 35 then orbits the substrate holder 32 about the axis B—B, and optionally rotates the substrate holder 32 about the axis C—C, to translate the substrate 12 across the planarizing surface 42. As a result, the abrasive particles and/or the chemicals in the planarizing medium remove material from the surface of the substrate 12.
The CMP processes should consistently and accurately produce a uniformly planar surface on the substrate assembly to enable precise fabrication of circuits and photopatterns. During the fabrication of transistors, contacts, interconnects and other features, many substrate assemblies develop large “step heights” that create a highly topographic surface across the substrate assembly. Such highly topographical surfaces can impair the accuracy of subsequent photolithographic procedures and other processes that are necessary for forming sub-micron features. For example, it is difficult to accurately focus photo-patterns to within tolerances approaching 0.1 micron on topographic substrate surfaces because sub-micron photolithographic equipment generally has a very limited depth of field. Thus, CMP processes are often used to transform a topographical substrate surface into a highly uniform, planar substrate surface at various stages of manufacturing the microelectronic devices.
One concern of CMP processing is that it is difficult to consistently produce a highly planar surface because the polishing rate and other parameters of CMP processing can vary across the substrate 12 during the planarizing cycle. The polishing rate can vary because properties of the polishing pad and/or the planarizing solution can change during a planarizing cycle. The polishing rate can also vary locally across the substrate surface because of non-uniformities in the (a) distribution of planarizing solution, (b) planarizing surface of the pad, (c) relative velocity between the pad and substrate assembly, and (d) several other dynamic factors that are difficult to monitor or evaluate during a planarizing cycle. The polishing rate even varies because the topography of the wafer changes during the planarizing cycle. Therefore, it would be desirable to be able to monitor and/or control at least some of these dynamic factors during a planarizing cycle.
One proposed technique for monitoring the status of a planarizing cycle is to measure static normal forces between the planarizing pad and the substrate. The normal static forces can be measured by placing an array of piezoelectric sensors laminated within a thin plastic sheet on the polishing pad, and then pressing the substrate assembly against the plastic sheet. The Tekscan Company currently manufactures a thin plastic piezoelectric array for this purpose. One drawback with the Tekscan device, however, is that the substrate must be disengaged from the polishing pad to place the piezoelectric array in the planarizing zone on the pad. The Tekscan device is thus generally used to take “before” and “after” measurements of a normal force distribution, but not during the planarizing cycle. The static normal forces measured by the Tekscan device when the substrate is stationary may not provide accurate and useful data because the static normal forces can be significantly different than the dynamic normal forces and shear forces exerted when the substrate 12 rubs against the planarizing surface 42 of the planarizing pad 40 during a planarizing cycle. The Tekscan device, therefore, may not provide accurate or useful data for monitoring and controlling a planarizing cycle.